Technical Field
The present disclosure relates to a barite filter cake removing composition and methods of removing a barite filter cake from a wellbore.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, is neither expressly nor impliedly admitted as prior art against the present invention.
To recover hydrocarbons (e.g., oil, natural gas), it is necessary to drill a hole in the subsurface to contact the hydrocarbon-bearing formation, such that hydrocarbons can flow from the formation into the wellbore and to the surface. Recovery of hydrocarbons from a subterranean formation is known as “production”. One key parameter that influences the rate of production is the permeability of the formation along the flowpath that the hydrocarbon must travel to reach the wellbore. Sometimes, the formation rock has a naturally low permeability, other times, the permeability is reduced during, for instance, drilling the well. When a well is drilled, a drilling fluid is circulated into the hole to contact the region of the drill bit, for a number of reasons—including, to cool the drill bit, to carry the rock cuttings away from the point of drilling, and to maintain a hydrostatic pressure on the formation wall to prevent production during drilling.
Drilling fluid is expensive particularly in light of the enormous quantities that must be used during drilling. Drilling fluid can be lost by leaking off into the formation, not only increasing the drilling costs, but also increasing the possibility of damaging the formation, since the drilling fines and other solids along wth the liquid in the drilling fluid may enter the formation, deposit in the pores of the formation, plug the flow channels, and reduce the permeability of the rock. To limit drilling fluid losses from the wellbore and protect the formation, the drilling fluid is often intentionally modified so that a small amount leaks off and forms a coating on the wellbore, or a “filtercake.”
For a filter cake to form, the drilling fluid must contain some particles of a size only slightly smaller than the pore openings of the formation. These particles are known as bridging particles and are trapped in surface pores, thereby forming a bridge over the formation pores. Filter cake building fluids can also contain polymers for suspension of solids and for reducing liquid loss through the filter cake by encapsulating the bridging particles. These can be either natural or synthetic polymers. The polymers can include one polymer such as xanthan selected for its rheological properties and a second polymer, a starch for example, selected for reduction of fluid loss. At completion of the drilling, however, the filter cake must be removed to allow production of the formation fluids or bonding of cement to the formation at the completion stage. Removal of the deposited filter cake should be as complete as possible to recover permeability within the formation.
The drilling fluid must also counter or suppress formation pressure. Therefore, the drilling fluid has to have enough density to balance formation pressure and keep the wellbore stable. Unbalanced formation pressure will cause an unexpected influx (also known as a kick) of formation fluids in the wellbore, leading to a blowout from pressured formation fluids. For this reason, weighting materials such as barite, iron oxides, and calcium carbonate are used in the drilling fluid, with barite being the most common for its desirable density, low production costs, and ease of handling. However, removal of barite containing filter cakes has been a challenging problem, since the conventional filter cake removal treatments utilizing an oxidizer (e.g. persulfate), hydrochloric acid solution, organic (acetic, formic) acid, or a combination of acid and oxidizer, although effective in removing calcium carbonate containing filer cakes, are ineffective in dissolving barite containing filter cakes. Barite, or barium sulfate, is insoluble in water or acid. Therefore, an urgent need exists in the drilling and completions sector for a reliable fluid for degrading barite filter cake efficiently and completely.